« PreviousContinue »
nerves from a ganglion, it has been thought that ganglia, by intercepting the direct communications between the brain and the extreme branches of nerves, might render parts thus supplied less' amenable to the will, and less under the influence of the general affeetions of the nervous system. It is also thought that ganglia might serve the office of subsidiary brains, each affording a separate source of nervous energy,
: , On the one hand, it ought to be ober served, that all the vertebral nerves, supplying parts over which the will exerts the most perfect control, have ganglia at their commencement; and that the nerves of the leg and arm form a plexus near their origin. The actions of the cremaster muscle are involuntary; yet I believe it is supplied by the same nerves, which supply muscles that are subject to Nør
luntary actions; therefore this opinion does not appear to me to be such as we should receive with entire confidence. Again, it it is further apparent, that the functions of the abdominal and other viscera are greatly affected by disorders of the brain, and that the brain is greatly affected by disorders of these viscera.
The ingenious and industrious French anatomist, Bichất, has classed the living functions into the organic and animal : the distinction seems a natural and useful one, and throws light on the physiology of the visceral nerve.
In vegetables, and in some moluscæ, no traces of a nervous system are discoverable. In some of the lower order of animals, that have organs for the preparation and distribution of nutriment, they are supplied by a visceral nerve, which it is probable maintains amongst those organs a con
currence of impressions and actions. In some of these animals no traces of nerves subservient to the voluntary regulation of their motions can
be found. In the ascending complexity of the nervous system, we find a nervous chord more or less beset with ganglia, which supplies other parts of the body besides the viscera, and which probably serves to maintain amongst them likewise a concurrence of impressions and actions. We next find at one end of this chord a kind of ganglion, or brain, which gradually becomes larger and more complex as we trace the series of links upwards to man, in whom it bears a much larger proportion to the nervous system in general than in any other animal.
other animal. The visceral nerve, in the ascending series of animals, appears connected with the animal nerves; and so numerous are these connections that this nerve bas in the human subject
obtained the title of the great sympathetic
The vital organs are required to carrý on their functions with a degree of regularity and order, under the varying circumstances of life; and the possession of a distinct nerve may enable them to continue their functions without so materially participating in the disturbances of the animal system, as they must otherwise have done : yet the numerous connections of the visceral with the animal nerves must render both participators in each other's disorders.
The nerves, then, may be said to proçeed from the brain, medulla spinalis, and visceral nerve, to all parts of the body for their supply. In thus expressing a fact, however, we should guard against an idea which the analogous distribution of
arteries is apt to engender. Arteries : be+ come minute in proportion as they send off branches, whilst on the contrary, the branches of nerves are often larger than the trunk from which they proceeded. It is no unfrequent occurrence for malformed children to be born without a brain, yet with a perfect nervous system. The most rational idea, therefore, we can entertain on the present subject, is, that the nerves are formed in the parts where we find them, and that they are connected to those parts of the organs from which we are accustomed to say they! proceed: Nerves are' vascular, and wel can inject them with subtile injections. :: i
The nerves, then, proceeding from, iar being connected with the brain, medula spinalis, and visceral nerve, may be tracedo ramifying throughout the body in the manner already mentioned, till they arrive